(1)2x^2-4x
=2x(x-2)
(2)4x^2-9
=(2x+3)(2x-3)
(3)x^2-4x+4
=(x-2)²
(4)(x+y)^2-14(x+y)+49
=（x+y-7)²
(5)(-2)^101+(-2)^100
=-2*(-2)^100+(-2)^100
=(-2)^100*(-2+1)
=-2^100